// Physical memory allocator, for user processes,
// kernel stacks, page-table pages,
// and pipe buffers. Allocates whole 4096-byte pages.

#include "types.h"
#include "param.h"
#include "memlayout.h"
#include "spinlock.h"
#include "riscv.h"
#include "defs.h"

#define PA2REF(pa) (((uint64)(pa)) / PGSIZE)
#define REFMAX     PA2REF(PHYSTOP)

void freerange(void *pa_start, void *pa_end);

extern char end[]; // first address after kernel.
                   // defined by kernel.ld.

struct run {
  struct run *next;
};

struct {
  struct spinlock lock;
  int    times[REFMAX];
} ref;

struct {
  struct spinlock lock;
  struct run *freelist;
} kmem;

void
kinit()
{
  initlock(&kmem.lock, "kmem");
  initlock(&ref.lock, "ref");
  freerange(end, (void*)PHYSTOP);
}

void
freerange(void *pa_start, void *pa_end)
{
  char *p;
  p = (char*)PGROUNDUP((uint64)pa_start);
  for(; p + PGSIZE <= (char*)pa_end; p += PGSIZE){
    ref.times[PA2REF(p)] = 1;
    kfree(p);
  }
}

// Free the page of physical memory pointed at by v,
// which normally should have been returned by a
// call to kalloc().  (The exception is when
// initializing the allocator; see kinit above.)
void
kfree(void *pa)
{
  struct run *r;

  if(((uint64)pa % PGSIZE) != 0 || (char*)pa < end || (uint64)pa >= PHYSTOP)
    panic("kfree");

  acquire(&ref.lock);
  if(--ref.times[PA2REF(pa)] == 0){
    
    // Fill with junk to catch dangling refs.
    memset(pa, 1, PGSIZE);

    r = (struct run*)pa;

    acquire(&kmem.lock);
    r->next = kmem.freelist;
    kmem.freelist = r;
    release(&kmem.lock);
  }
  release(&ref.lock);

}

// Allocate one 4096-byte page of physical memory.
// Returns a pointer that the kernel can use.
// Returns 0 if the memory cannot be allocated.
void *
kalloc(void)
{
  struct run *r;

  acquire(&kmem.lock);
  r = kmem.freelist;
  if(r)
    kmem.freelist = r->next;
  release(&kmem.lock);

  if(r){
    memset((char*)r, 5, PGSIZE); // fill with junk
    // acquire(&ref.lock); // 这里不能加锁因为kcopy里面也会调用kalloc,kcopy里面已经加锁了
    ref.times[PA2REF(r)] = 1;
    // release(&ref.lock);
  }
  return (void*)r;
}

void
refinc(void *pa)
{
  acquire(&ref.lock);
  ref.times[PA2REF(pa)]++;
  release(&ref.lock);
}

int
reftimes(void* pa){
  return ref.times[PA2REF(pa)];
}


void*
kcow(void *pa_old){
  acquire(&ref.lock);
  if (ref.times[PA2REF(pa_old)] <= 1){
    release(&ref.lock);
    return pa_old;
  }
  uint64 pa_new = (uint64)kalloc(); 
  if (pa_new == 0){
    release(&ref.lock);
    return 0;
  }
  memmove((void*)pa_new, pa_old, PGSIZE);

  ref.times[PA2REF(pa_old)]--;
  release(&ref.lock);
  return (void*)pa_new;
}